Musical instrument employing single unijunction transistor oscillator in which volume is controlled by key displacement



Oct. 21, 1969 J. DESTELLE 3,474,182

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MUSICAL INSTRUMENT EMPLOYING SINGLE uNIJuNcTIoN TRANSISTOR OSCILLATOR IN WHICH VOLUME 15 CONTROLLED BY KEY DISPLACEMENT Filed April 8. 1966 5 Sheets-Sheet 2 a n Ina-71::

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MUSICAL INSTRUMENT EMPLOYING SINGLE UNIJUNCTION TRANSISTOR OSCILLATOR IN WHICH VOLUME 15 CONTROLLED BY KEY DISPLACEMENT Filed April 8, 1966 5 Sheets-Sheet 4 O -=a 35 I Oct. 21, 1969 J. DESTELLE 3,474,182

1 MUSICAL INSTRUMENT EMPLOYING SINGLE UNIJUNCTION TRANSISTOR OSCILLATOR IN WHICH VOLUME IS CONTROLLED BY KEY DISPLACEMENT Filed April 8, 1966 5 Sheets-Sheet /65 WWI" f;

ean De:ze//e United States Patent MUSICAL INSTRUMENT EMPLOYING SINGLE UNIJUNCTION TRANSISTOR OSCILLATOR IN WHICH VOLUME IS CONTROLLED BY KEY DISPLACEMENT Jean Destelle, Dieppe, Seine Maritime, France, assignor to Armel Arts, Mecanique Electronique, Paris, France, a corporation of France Filed Apr. 8, 1966, Ser. No. 541,167

Claims priority, application 7France, Apr. 14, 1965,

Int. Cl. olh 1/04 U.S. Cl. 84-125 8 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved electronic musical instrument which is very easy to operate, since it has very small dimensions and does not depend on an external electric current supply. The instrument according to the invention also permits a large number of different effects of timbres and sound expressions.

The instrument according to the invention may be constructed in monodic or polyphonic forms. In the monodic construction the invention enables the player to imitate the majority of the conventional melodic instruments of an orchestra, thus enabling him to replace a number of different musicians. It follows that a musical group comprising a number of players each using the instrument according to the invention can produce more varied effects than a large group combining numerous conventional instruments.

In its polyphonic form of construction the invention provides a complete instrument of the electronic organ family, with extremely wide possibilities.

One of the disadvantages of known electronic musical instruments is that the player must adjust the intensity of sound either by a pedal or by a knee control, thus making it practically impossible to play a piece standing or while moving. The invention relates more particularly to an instrument comprising a system of expression which makes the intensity of sound produced dependent on the pressure applied by the player to the corresponding key. It follows that by a single hand the player can obtain a style of playing utilizing all nuances of sound intensity.

As a result, the instrument according to the invention can be used in the small groups used formodern rhythmical music in which the mobility of the artist permits on the one hand a spectacular choreographical effect and on the other hand effects of modulation of the spatial sound volume resulting from the movement of the directional axes of the sound generator. These possibilities, which are used considerably by certain artists, are impossible with any fixed instruments, that is to say with all electronic instruments known at the present time.

Moreover, having regard to the fact that the instrument according to the invention can be played by one hand, and that its small dimension enable a plurality of similar instruments to be juxtaposed, the artist can play two different instruments at the same time, of which one may be monodic and the other polyphonic, or both may be of "ice the same kind. It is easy to imagine the immense possibilities provided by this simultaneous utilization of a plurality of instruments.

In particular, the selection of a polyphonic accompaniment instrument for the low notes to be played by the right hand, whereas the higher pitched voice part is interpreted by the left hand on a second instrument, is a new possibility for the left-handed musician.

In a general way, the instrument according to the invention comprises essentially at least one musical frequency oscillator, optionally a vibrato oscillator acting on said musical frequency oscillator, an expression circuit connected to the latter, and then, in series, a timbre circuit, a preamplifier, and a power amplifier.

The musical frequency oscillator advantageously utilized according to the invention makes use of a unijunction transistor which supplies an extremely stable frequency and which is moreover separately fed by a selfcontained generator, preferably a dry battery, to which it is connected by its two bases.

In the supply circuit of the unijunction transistor a rheostatic arrangement is provided which enables the instrument to be tuned. The single rheostat used makes it possible not only to tune the instrument but also to obtain glissando effects, the axis of the rheostat being frictionally mounted. The signal coming from the vibrato oscillator, if provided, is applied to the musical frequency oscillator at a point in the aforesaid supply circuit.

The emitter of the unijunction transistor is connected to one pole of the generator by a group of capacitors adapted to be switched in parallel by the keys of the instrument keyboard, and to the other pole of the generator through a network of resistors in series and of associated switches, each switch being connected mechanically to a key of the keyboard, the signal obtained at the transmitter being transmitted through the medium of a capacitor to the base of a transistor in a common-collector connection.

In the monodic form of construction the instrument utilizes a single unijunction transistor with the above-described associated components. In the polyphonic construction a plurality of individual oscillator assemblies, preferably five oscillators, are connected, each oscillator utilizing the electronic components associated with it, that is to say essentially a unijunction transistor, a group of capacitors and a reduced number of resistors, a note played requiring only a tuning resistor.

An important feature of the instrument according to the invention consists in the arrangement of the expression circuit. The signal coming from at least one musical frequency oscillator is transmitted through the medium of a capacitor to a diode, the polarization of which is varied by means of the current supplied by a photosensitive element subjected to the action of a light beam, a movable screen being interposed between the source of said beam and said element, said screen being connected mechanically to an expression bar participating in the individual displacements and the depth of depression of each key of the keyboard.

This arrangement is distinguished by its simplicity and effectiveness as compared with previously known instruments which made use of valve circuits, particularly triode circuits, in which expression was achieved for example by modifying the polarity of the triode or the slope of its characteristic.

The invention also provides for the association of the oscillator control circuit with an expression circuit essentially utilizing a diode, which is more economical. The polarization of the diode varies in dependence on the pressure applied by the player to the keyboard keys, thus modifying in a corresponding manner the desired volume of sound.

The expression circuit may also be connected between the oscillator circuit and the timbres circuit, or else between the two stages of the preamplifier circuit.

Another, equally simple solution provided by the invention for forming the expression circuit is the utilization of a photoresistive element as a connection element. The photoresistive element is then illuminated by the light source and the intensity of the lighting can be modified in the manner previously described.

The light source may advantageously be composed of a small neon lamp fed by an oscillator-converter supplying a high voltage of supersonic frequency, so that its consumption of low voltage current from the battery is extremely small and consequently no filtration of the conversion frequency is necessary.

It should also be noted that the light source co-operating with the photosensitive element is optionally taken out of circuit when the instrument is not in use, in order to avoid excessive current consumption, despite the very low power required by the source. When the player applies pressure to a key, a contact is closed and brings the light source into action.

Moreover, the instrument may also be used with complete disconnection of said light source. In this case the expression cannot be modified; it is said that the plane of the instrument is flat.

The signal coming from the expression circuit is applied to a distortion or timbres circuit, which supplies a low current signal. This signal is then amplified. In one advantageous embodiment of the invention the preamplifier stage, which comprises essentially two transistors in common emitter connection, comprises a silence circuit intended to cancel the collector current of the transistor to which the input signal is applied, when no key is depressed, said silence circuit comprising essentially a transistor and a switch connected mechanically to the expression bar.

The electronic components of the instrument according to the invention are particularly suitable for arrangement in the form of printed circuits, that is to say lines of conductive metal engraved on an insulating plate. This advantageous form of construction supplies an instrument of extremely small dimensions.

The utilization of printed circuits according to the invention also permits a large variety of combinations, thanks to the various possible forms of switching of the contacts used in each member. For this purpose the invention provides a switching device adapted to be used in conjunction with a printed circuit. This device comprises essentially an insulating bar mounted for rotation about its longitudinal axis and equipped on its periphery with a certain number of conductor blades adapted to come into contact, under the effect of the rotation of the bar, with the lines of the printed circuit corresponding to the desired switching operations, the rotation of the bar being effected, against the reaction of elastic means, with the aid of a lever one end of which is mounted for pivoting about a fixed axis and the other end of which has a slope engaging in a resiliently retractable bolt, said lever being provided with operating means for the purpose of applying it against the bar in order to impart a rotational movement thereto.

In the case of the instrument of the invention, it is the keys of the timbres conttactors which constitute the means of operating the lever. The resilient bolt may be common to a plurality of levers, each of said levers being solid to a separate key.

The invention is described hereinbelow by way of illustration and without limitation of any kind, with the aid of an example of construction of the instrument and with reference to the accompanying drawings, in which:

FIGURE 1 is a diagrammatic view in perspective showing the shape of the instrument,

FIGURE 2 is a diagram showing the assembly of all the electronic components of the instrument,

FIGURE 3 illustrates the circuit of a musical frequency oscillator in a monodic instrument,

FIGURE 3a is a diagram showing the coupling of oscillators of the type illustrated in FIGURE 3, for a polyphonic instrument,

FIGURE 4 is a diagram of the expression circuit,

FIGURE 5 shows in perspective the arrangement of the expression bar,

FIGURE 6 shows a possible diagram for the timbres circuit,

FIGURE 7 shows a preamplifier equipped with the silence device,

FIGURE 8 shows an amplifier circuit arrangement,

FIGURE 9 is a diagram of a very low frequency oscillator capable of being used as vibrato generator,

FIGURE 10 shows the arrangement on a printed circuit of all the electronic components of a monodic instrument,

FIGURES l1, l2 and 13 relate to a switching device making it possible to select a given timbre by operating a single key, FIGURE 11 showing this device in perspective,

FIGURE 12 showing the device in section, while FIG- URE 13 shows a detail of the device,

FIGURE 14 shows an alternative expression circuit containing a photoresistor,

FIGURE 15 shows an oscillator converter circuit feeding a neon lamp, and

FIGURE 16 shows a switch system controlled by the keys of the keyboard.

As can be seen in FIGURE 1, the instrument is in the form of a box having on the top a keyboard 1, for example comprising 25 keys, disposed in similar manner to those of a piano, and provided with a group of octave keys 2 and a group of timbres contactors 3. The depression of one of these keys operates the instrument.

The depression of an octave key 2 decides the general pitch of the sound produced by the instrument; this pitch may thus be displaced by one octave at a time, or by several octaves, and cover the entire range usual in a piano keyboard.

A button 4 enables the mean intensity of sound to be adjusted. A sliding bar device 6 enables the pitch of the sound to be varied continuously by at least a halftone. This system enables an experienced musician to adjust the sound produced if desired, so as to correct variations of the correct pitch due to enhanced harmony and to superimpose on his playing an effect of slow frequency modulation or a glissando effect.

A spindle 5 enables the instrument to be tuned to the pitch of the other instruments in the case of group playing.

One or more keys 7, or else a bar covering the entire length of the keyboard, permits regulation of the expression system.

The loudspeaker or loudspeakers is or are preferably fixed on the bottom or side walls of the box.

FIGURE 2 shows the fundamental diagram of the electronic system, which comprises essentially at least one preamplifier 13 and a power amplifier 14.

FIGURE 3 shows the diagrammatical constitution of the relaxation oscillator which may be used in the monodic version of the instrument. In the embodiment illustrated, the circuit utilizes a unijunction transistor, this type of circuit being well known for its frequency stability and producing periodic voltages assuming the form of pulses or of sawteeth which are very rich in harmonics.

The frequency stability of this oscillator may be improved in practice by utilizing an independent supply to feed the oscillator alone. This supply may come from a dry battery, the low output of which does not give rise to substantial variations of voltage within a reasonable period of time, or else from a quasi-constant discharge voltage battery for example of the mercury type. Voltage stability could also be obtained by any other conventional arrangement using a Zener diode or a gas diode.

As illustrated in FIGURE 3 the unijunction transistor is connected by its two bases to a battery 19 through the medium of a switch 20 and of the two resistors 16 (for example of 22 ohms) and 17 (for example of 100 ohms) and of the reostat 18 (for example of a maximum value of 1000 ohms). This rheostat, the capacitor 38 of which effects the uncoupling, makes it possible to vary the voltage at point 36 and assumes two functions: the tuning of the instrument and the variation of frequency by means of the glissando bar 6.

An alternating current voltage of very low frequency coming from the vibrator oscillator circuit 10 may also if desired be applied to the point 36, thus effecting a frequency modulation of the musical frequency oscillator.

The emitter of the unijunction transistor is connected on the one hand to the negative pole of the supply battery through a capacitor or a group of capacitors 21, 22, 23, 24 which are adapted to be switched in parallel by means of the keys 2, and on the other hand to the positive pole by a network of resistors 27, 28 35 connected in series and the switches 39, 40, 41 44. The resistors 32, 33, 34, 35 have increasing values and follow a geometrical progression at a rate equal to the twelfth root of 2.

Each of the switches 39, 40 44 is connected mechanically to a key on the keyboard. The depression of one of these keys closes the circuit between the emitter and the positive pole through the medium of at least one of the resistors of the group of resistors 31 35 the value of this resistance being R. The depression of one of the push-buttons 2 brings into circuit one or more of the capacitors 21, 22, 23 the total capacity of which is C.

The resultant frequency oscillation is therefore inversely proportional to the product RXC.

The signal taken from the emitter of the unijunction transistor is transmitted through the medium of a capacitor 37 to the base of a transistor 46 which for example is in a common-collector connection, so as to have a high input impedance. The base of this transistor is polarized by a resistor 48, while a resistor 47 constitutes the load.

A capacitor 49 makes the connection with the expression circuit, which will be described in detail with reference to FIGURE 4.

In the case of a polyphonic instrument, a plurality of oscillator assemblies must be used, each of which may be in accordance with the diagram in FIGURE 3.

In order to reduce the size and cost price of the instrument, it is possible to dispense with a small number of dissonant harmonic combinations little used in music and to accept a limit of five oscillators, each of which produces one or the other of three neighbouring notes per octave.

The diagram in FIGURE 3a shows by way of example how five oscilators O1, O2, O3, O4, 05 may be associated in this manner.

The oscillator 01 can play any of the following six notes: C, C sharp and D in the first octave, and D sharp, E, F in the second octave. Similarly, the oscillators C2 and 03 are each associated with six notes, the oscillator 04 with four notes, and the oscillator 05 with three notes.

The example selected is limited to two octaves for reasons of size, but the invention may obviously extend to any number of octaves.

It will be seen that this arrangement makes it possible to produce simultaneously the different notes of the majority of chords in current use. Taking C as basis, it is possible to obtain (amongst others).

Perfect major chordzC, E, G, C, C. Perfect minor chordzC, Eb, G, C, C. Diminished 5th chord:C, Eb, Gb. Augmented 5th chordzC, Eb, Gb. Augmented 5th chordzC, E, G sharp. Dominant 7thzC, E, G, Bb.

Dominant 9thzC, E, G, Bb, D. SixthcC, E, A.

Similarly, it is also possible to play diminished 7th and 9th chords and numerous other combinations. Only certain simultaneous appoggiatures and certain seconds cannot be rendered; aescetically their execution is a sustained note (which is the case with electronic instruments in general) is moreover extremely hard because of the very rapid beats which they cause.

In the instrument according to the invention each key brings into circuit a contact connecting to the positive pole an assembly of resistors in series. If two keys are operated at the same time and if both correspond to resistors forming part of the circuit of the same oscillator, only the highest of the two notes played will be heard.

Consequently the playing of any piece of music on the instrument in its polyphonic version can at most cause the fugitive elimination of a note of a chord, and it will be understood that only a very expert musician can as a rule hear the difference in tone.

In practice, an arrangement utilizing five oscillators therefore permits very convenient polyphonic playing, provided however that only one hand plays on a single keyboard.

For the execution of more complete musical works, the use of two instruments, one for each hand, is possible. The right hand instrument may moreover be monodic in the case where there is a single monodic line (song).

The use of five oscillators disposed in accordance with the invention therefore utilizes a reduced number of com ponents, because there is only one tuning resistor per note. The capacitors 21, 22, 23 are obviously individual to each oscillator, and their switching over must be simultaneous when a change of octave is made.

FIGURE 4 illustrates a possible type of circuit intended to effect expression. The capacitor 49 transmits the signal of the oscillator to a diode 50 loaded by a resistor 52 and polarized by a resistor 51 which polarizes the anode of diode 50 positive relative to the cathode. The characteristic of a crystal diode not being linear, the variation of intensity of the signal at the input of the capacitor 64, which constitutes the connection to the timbres circuit illustrated in FIGURE 6, is obtained by varying the polarization of the diode 50. There are obviously numerous possible modes of variation of the polarization of the diode.

According to an advantageous feature of the invention, use is made of a photoelectric circuit to permit regulation of the sound volume which it is desired to obtain in dependence on the pressure applied to the keyboard keys. In FIGURE 4, where this circuit is illustrated in detail, the photosensitive element is designated by the reference 54. As can be seen from the drawing, if the switch 56 is closed and the switch 55 is open, the photosensitive element 54, which may be a photodiode or a photoresistor, transmits through the resistor 53 a current the intensity of which is dependent on its illumination. A low consumption bulb 63 is situated opposite the photosensitive element, and a movable screen 62 permits the illumination thereof to be adjusted.

Referring to FIGURE 5, it is seen that the screen 62 is connected mechanically to a bar 66 which is situated beneath the keys of the keyboard and covers the entire range of the latter. The depression of any key on the keyboard therefore eifects the displacement of the bar and consequently modifies the illumination of the photosensitive element, thus varying the polarization of the diode 50.

Subsidiarily, a switch (not illustrated in FIGURE 4) connected mechanically to the expression bar 66 can interrupt the current in the bulb 63 when no key is depressed. Similarly, in order to avoid any parasitic spitting effect when contact is made, this switch may be situated in the base circuit of a transistor, the emitter-collector 7 circuit of which feeds the filament of the bulb. These various additional arrangements make it possible to reduce considerably the consumption of the apparatus by cancelling the bulb heating current during rest periods.

Referring again to FIGURE 4, it is seen that when both the switches 55 and 56 are closed, the resistor 65 shunts the photoresistive element 54. The sensitivity of expression is thereby considerably modified and through a suitable selection of the value of the resistance 65 in dependence on the characteristics of the photosensitive element 54 and of the diode 50 on the one hand, and on the law of variation of illumination on the other hand, it is possible to obtain a very rapid mode of attack, comparable to that of a trumpet, for example. On the other hand, the opening of the switch 55, by simple variation of the depth to which the key is depressed, permits very varied effects ranging from pianissimo to forte.

Independently of the keys of the keyboard, one or more expression keys 7 may be provided to permit operation of the bar 66 without releasing the oscillator. Thus the left hand may for example control the expression of the piece played on the keyboard by the right hand.

Referring to the right hand part of the diagram in FIGURE 4 it will be seen that the opening of the switch 56 brings into action the percussion circuit formed by the capacitors 59 and 60-, the resistor 58, and an inverter 57.

The common pole of the inverter 57 is connected mechanically to the expression bar. When no note is played, this bar is raised and the capacitors are charged. When a key is depressed, the common pole of 57 is connected to the polarization circuit of the diode 50 and the capacitors are discharged into that circuit. The law of variation of discharge current being decreasing, this produces a plucked or struck string effect. The switch 61 makes it possible to shunt the capacitor 60 and thus to vary the total capacity of the group of capacitors 59-60, and therefore the duration of the dying down of the sound.

The selection of the values of the elementary components of this circuit has an influence on modes of attack; very great variations can thus be obtained.

As shown in FIGURE 14, the expression circuit may moreover be composed of a photoresistor which transmits the signal between two stages. In this case the percussion effect cannot be obtained by means of this circuit alone.

The resistance of the photoresistive element 157 varies in dependence on the illumination which it receives from the lamp 159, which illumination is made variable by the displacement of the screen controlled by the expression bar.

FIGURE 15 shows a possible diagram of a transistor oscillator-converter, which may be used to convert the low voltage supply current into an alternating high tension current of supersonic frequency, feeding a small neon tube.

The current in the tube is limited by the resistor 163. 164 is a voltage transformer the secondary of which feeds the lamp. The primary of this transformer is composed of the coupled windings which, together with the transistor 165, the capacitor 167, and the resistor 166, form the oscillator circuit.

The supersonic frequency is selected so that no audible fraction of the modulation produced by the oscillator converter will reach the ear of the listener.

Referring again to FIGURE 4, the capacitor 64 effects the connection to the following circiut, which is the deforming circuit intended to modify the timbre, of which one example of construction is illustrated in FIGURE 6.

This circuit may have a large number of forms, which are all intended to produce definite distortions in the signal, favouring the transmission of certain frequencies, either by filtering effect, or by a resonance effect. FIG- URE 6 shows one of the diagrams which may be utilized for this purpose.

In this figure the references 67, 68 and 69 designate different self-induction coils. The references 70, 71, 72, 73, 74, 75 and 76 designate capacitors of progressively increasing capacity (for example from 2,000 to 200,000 pf.) and the references 77, 78, 79, 86, 86 relate to switches which may be closed in any combination. Depending on the combination selected, the circuit produces certain resonances, which may advantageously be similar to those which actually exist in conventional musical instruments. This process makes it possible to give to the sounds a timbre very close to that of numerous instruments.

The switches 77, 86, 86 may be operated by independent push-buttons 3 or else, in an alternative form of the instrument, the group of these switches may be replaced by a multiple contactor of the type which will be described later on with reference to FIGURES 11, 12 and 13.

The musical frequency signal taken at is a weak current, which requires to be amplified, either in a circuit outside the apparatus, which is permitted by the instrument, or, according to a preferred embodiment of the invention, by means of an amplifier assembly contained in the box itself.

The description of the amplifier assembly is given below purely by way of indication, because these are generally circuits well known to those versed in the art and other solutions could be just as suitable.

FIGURE 7 illustrates a preamplifier which may for example be used and which is essentially formed by two transistors 89 and 100 in a common-emitter connection. An inherent feature of the invention comprises the circuit 87, which has been enclosed by a rectangle of broken lines. This circuit in fact constitutes a rest device intended to cancel the connector current of the transistor 89, to which the conductor 85 is connected when no key is operated. The switch 96 is connected mechanically to the expression bar 66, and is closed only if a, key is depressed. In this latter case, after passing through the resistor the base current renders the emitter-collector space of the transistor 94 conductive, and consequently the collector of the transistor 89 is connected to the negative pole of the source through the load resistor 92 and the transistor 94. The emitter-collector space of the transistor 94 is shunted by a high capacity capacitor 93 so as not to allow any alternating component to intervene in this rest circuit.

This arrangement ensures completely silent switchingover and, during musical silences, permits absolute elimination of background noises, interference, and humming of any origin which a high gain amplifier would not fail to pick up under certain conditions of use.

The transistors 89 and in a common-emitter connection form two amplifier stages, the load of the last of said stages being constituted by a potentiometer 103 which, when operated by the button 4, enables the general sound level to be regulated.

FIGURE 8 shows purely by way of illustration an amplifier which may be used as output circuit in the invention and which is connected to the output of the preamplifier which has just be described.

The circuit arrangement illustrated in FIGURE 8 is well known and its realization calls for no comments. It has been selected in preference to any other because of its simplicity and the small space which it requires.

The transistor 106 is of the low frequency PNP type. The transistor 111 is of the N-P-N type, symmetrical to the N-P-N transistor 114. The transistors and 113 are two medium power transistors of very similar characteristics.

As the power stage is constituted by a class B pushpull circuit, current consumption is very approximately proportional to the acoustic power supplied. This results in a longer battery life, the lower the power at which the instrument is used. i

The vibrato oscillator 10, the circuit of which is illustrated in FIGURE 9, supplies a very low frequency alternating current, the frequency and intensity of which 9 are adjustable. As has been previously mentioned, this current is introduced at the point 36 of the oscillator (FIGURE 3) and gives rise to adjustable modulation of deviation frequency and frequency.

In practice, it is simple to retain only two speeds and two possible vibrato frequencies, which nevertheless makes it possible to multiply by 5 the number of variations of timbre.

FIGURE 9 shows by way of example the diagram of an oscillator which may be used for this purpose in the instrument. This is an oscillator of the phase shift capacity-resistor network type, which supplies an approximately sinusoidal voltage.

The resistors 125 and 126 are adjustable and enable the vibrato frequency to be adjusted: similarly, the resistors 135 and 137 are adjustable and enable the vibrato amplitude to be varied.

The switches 138 and 139 control respectively frequency and amplitude changes. The output 140 is connected through the medium of a switch 141 to the point 36 in the oscillator circuit illustrated in FIGURE 3.

All the circuits of the apparatus may be fed either by dry (or other) batteries, or by an accumulator of small volume, the recharging device of which may be situated in the box of the instrument. In this case, the battery is preferably recharged outside the periods during which the instrument is used, in order to enable the latter to retain its self-contained nature.

The various supply circuits of the different stages of the apparatus are suitably uncoupled by resistor-capacitor circuits, in order to avoid any interference entailing the risk of causing self-oscillation of the amplifier stages.

For the material realization of the circuits described above, use may be made of one or more insulating material plates covered with engraved conductive metal, commonly known as printed circuits. The simplest arrangement, which is preferably adopted in the invention, is one which groups together on the same plate all the circuits of the instrument, including the poles of the switches and connectors, as illustrated in FIGURE 10. This last-mentioned figure shows the complete diagram of the printed circuit with the corresponding references of the electronic components described above. The outside connections to the printed circuit are then extremely few in number, and effect for example the connections to the loudspeakers and to the supply generators.

It is also possible to utilize resistors obtained by direct photo engraving on the engraved circuit, as tuning resistors for the oscillators.

The switches 77, 78 86 of the timbres circuit in conjunction with those of the vibrato circuit and those of the percussion circuit, permit an extremely varied series of combinations.

The switches 39, 40 44 in FIGURE 3, each of which corresponds to a note played, may be constituted, as illustrated in FIGURE 16, by flexible steel blades 168 carrying contact points 169 of precious metal.

Each key 175 is returned upwards by a spring 171. A permanent magnet 172 is fixed to the end of this spring.

When the key 175 is depressed lightly, the magnet 172 comes into contact with the printed circuit plate 173 and moves towards a small soft iron core 174. This core channels the lines of force of the magnet field and the blade 168 is strongly attracted towards the magnet, abruptly closing the circuit between the blade 168 and the contact 170 fixed on the board 173.

If the key is depressed more deeply, the contact is maintained and the spring 171 opposes a greater depressing force, because its two ends then rest on a fixed surface.

When the key is raised, the magnet 172 is lifted and the elastic return force of the spring 168, as soon as it becomes greater than the attraction force due to the magnet, effects the abrupt breaking of the contact.

All the blades 168 and the contact studs may be enclosed in a fluid-tight casing 176 which prevents any pollution of the contacts. The space inside this casing may if desired be evacuated and optionally may be filled with a neutral gas.

As an alternative, the magnet 172 may be fixed directly on the key 175, either rigidly or through the medium of a spring device similar in effect to the spring 171.

In order to simplify the utilization of the instrument, it is advantageous for all the fitting operations necessary for obtaining a clearly defined tone to be eflected with the aid of a single device.

This may be achieved by associating n switches with n complete deforming circuits, but through the complication which this entails and the number of components utilized this solution very quickly limits the number of possible timbres.

The device illustrated in FIGURES 11 to 13 makes it possible to effect in a simple manner the simultaneous switching of a large number of circuits, and its application is not limited solely to the instrument of the invention.

On the plated insulating plate 147 there are formed conductive bands shown in the form of thin hatched bands in FIGURE 11 and alternating with insulating bands. Each of the conductive bands is connected to one of the poles to be switched. For example, the conductive bands 142 and 143 may be connected to the poles of a switch. An insulating bar 148, mounted to pivot about an axis 149 perpendicular to the conductive bands, is equipped with flexible metal blades 150. The rotation of the bar about its axis in the direction of the arrow, under the action of a pressure applied by the end 152a of the push-rod 152 (not illustrated in FIGURE 11 but seen in section in FIGURE 12), brings the metal blades into contact with the conductive blades 142, 143 thus making sliding contact. The bar is returned to its original position by a spring 151, and its operation is effected by a push-rod 152, which can in turn be locked by a bar 153 pivoting about an axis 154, as shown by FIGURES 12 and 13, FIGURE 12 being a section through the device in a plane passing through the line XIIXII in FIGURE 11 and perpendicular to the plate 147.

A plurality of bar-push-rod assemblies may be disposed side by side so as to permit various switchings between the conductive bands. The locking bar 153 may be common to a plurality of keys, and the shape of the locking catch 155 may be designed so that the operation of one key frees the other keys of the same group (FIGURE 13).

A switch thus arranged may advantageously be used in an electronic musical instrument and one key associated with each timbre desired. The corresponding bar 148 is provided with the desired number of metal blades occupying the selected position so as to effect the electrical connection between the corresponding conductive bands. Each of the bands is connected to a pole to be switched. In the instrument of the invention these poles may be those of the switches 70, 71 76, 55, 56, 61, 138, 139, 141, for example.

The position of the contact blades may also be modified as desired by the user, thus making it possible when desired, to use a certain number of original timbres and modes of expression which will thus to some extent be personalized.

I claim:

1. An electronic musical instrument comprising essentially at least one musical frequency oscillator, optionally a vibrato oscillator acting on said musical frequency oscillator, an expression circuit connected to the latter, and then, in series, a timbres circuit, a preamplifier and a power amplifier, said instrument being characterized in that the musical frequency oscillator comprises at least one unijunction transistor which supplies an extremely stable frequency and which is fed by a stabilized voltage generator to which it is connected by its two bases, the emitter of the unijunction transistor being connected to one pole of the generator by a group of capacitors adapted to be switched in parallel by keys of the instrument and to the other pole of the generator by a network of resistors in series and of associated switches, each switch being connected mechanically to a key of the keyboard, the signal taken from the emitter being transmitted through the medium of a capacitor to the base of a transistor in a common-collector connection, the signal com: ing from said musical frequency oscillator being transmitted, through the medium of a capacitor, to a diode the polarization of which varies in dependence on the current supplied by a photosensitive element subjected to the action of a light beam, a movable screen being interposed between the source of said beam and said element, said screen being connected mechanically to an expression bar participating in the individual displacements and the depth of depression of each key of the keyboard, the signal coming from said expression circuit being applied to a distortion circuit or timbres circuit which issues a weak current signal, which is previously amplified in a preamplification stage which comprises essentially two transistors mounted in a common-emitter connection and a silence circuit intended to cancel the current of the collector of the transistor to which the input signal is supplied, when no key is operated, said silence circuit comprising essentially a transistor and a switch connected mechanically to the expression bar.

2. An instrument according to claim 1, characterized in that the supply circuit of the unijunction transistor includes a rheostat arrangement which permits the tuning of the instrument.

3. An instrument according to claim 2, characterized in that the rheostat arrangement consists of a single rheostat the axis of which is frictionally mounted both for the purpose of tuning the instrument and for obtaining glissando effects.

4. An instrument according to claim 1, characterized in that the signal coming from the vibrato oscillator, if

12 provided, is applied to the musical frequency oscillator at a point in its supply circuit.

5. An instrument according to claim 1, characterized in that the musical frequency oscillator comprises a single unijunction transistor, in which case the instrument is monodic.

6. An instrument according to claim 1, of a polyphonic character, characterized in that a plurality of oscillator assemblies, preferably five individual oscillators are connected, each utilizing the electronic components which are associated with it, that is to say essentially a unijunction transistor, a group of capacitors, and a reduced group of resistors, a note 'played requiring only one tuning resistor.

7. An instrument according to claim 1, characterized in that the light source cooperating with the photosensitive element is switched off when the instrument is not in use.

8. An instrument according to claim 1, characterized in that each switch associated with a key of the instrument adapted to a printed circuit consists of an elastic blade fixed at one end to the support of the printed circuit and carrying at its other end a contact adapted to be brought into and put out of action by a conductive element of the printed circuit, and in that each key is subjected to the action of a spring normally urging it away from the support of the printed circuit, said spring being fixed at one end on said support and carrying at its other end a permanent magnet adapted, under the effect of the displacement of the key, to cooperate with a soft iron member solid to the support of the printed circuit, in order to make or break the passage of current between the contact of the blade and the printed circuit.

No reference cited.

HERMAN KARL SAALBACH, Primary Examiner F. P. BUTLER, Assistant Examiner U.S. C1. X.R. 841.27; 331-111 

